In recent years, display devices have developed remarkably. Various display devices including LED display devices and EL display devices have been introduced into various OA apparatuses such as PCs and word processors. These display devices each have a structure in which a display element is interposed between transparent conductive films.
Currently, indium tin oxide (ITO) films constitute a mainstream of the conductive transparent film, since ITO films have excellent transparency, low resistance, good adhesion to a substrate, or the like. Generally, ITO films are prepared by the sputtering method.
ITO films have such a disadvantage that, since a strong acid is used for etching, other films or underlining structures, for example, a wire such as aluminum used in a gate line or a source/drain line in the case of a thin film transistor liquid crystal display device (TFT-LCD), may be damaged. On the other hand, attempts have been made to etch with a weak acid by forming an amorphous ITO film at low temperatures. However, ITO has an increased resistance in an amorphous state. In addition, controlling sputtering conditions for forming an amorphous ITO film is very difficult, and hence, has become a problem encountered during a production process.
To solve the above-mentioned problem, Patent Document 1 discloses a sputtering target formed of indium oxide and zinc oxide. Patent Document 2 discloses an amorphous transparent conductive film formed of indium oxide and zinc oxide.
The amorphous transparent conductive film is excellent in etching workability with a weak acid and exhibits excellent properties remaining no etching residues. However, it is known that, due to the amorphous nature, the surface of the conductive film becomes a thin film having a layer with a high resistance.
Due to the presence of the high-resistance layer on the surface, there is a possibility that a problem such as generation of a contact resistance between the transparent conductive film and an anisotropic conductive film (ACF) for connecting a TFT-LCD substrate and an external circuit or between the transparent conductive film and a probe for examination may occur.
Patent Document 1: JP-A-6-234565
Patent Document 2: JP-A-7-235219
The invention has been made in view of the above-mentioned problems. An object of the invention is to provide an amorphous transparent conductive film having a high degree of conductivity in which the resistance of a resistance layer on the surface of the conductive film is low, as well as to provide a method for producing the same.